In recent years, from growing interest in environment/energy, there has been a great need for industrial products related to energy saving and, as one of these, glass and a film that are effective for heat shielding of window glass of houses, automobiles and the like, that is, for reducing a thermal load by sunlight are required. In order to reduce a thermal load by sunlight, it is necessary to prevent the transmission of sunbeam either in a visible light region or in an infrared region of the solar spectrum. In particular, as to windows for automobiles, high transmittance for the visible light region is required from the viewpoint of safety, and a demand for heat shielding is also high, and there is also a movement to regulate insolation reflectivity in some countries.
What is used frequently as eco-glass having high heat insulating/heat shielding properties is a multilayered glass coated with a special metal film that shields heat radiation, which is referred to as Low-E pair glass. The special metal film can be made by laminating a plurality of layers by, for example, a vacuum deposition method. These coatings of a special metal film made by a vacuum deposition are extremely excellent in reflection performance, but a vacuum process has a low productivity and requires high production cost. Furthermore, through the use of a metal film, electromagnetic waves are shielded at the same time, and thus there are such problems as causing electromagnetic obstruction in the case of using a mobile phone or the like and making ETC useless when the film is used for automobiles. Moreover, in addition to the electromagnetic obstruction, windows of automobiles are also required to have high transmittance for the visible light region from the viewpoint of safety.
On the other hand, there is proposed a method that utilizes a cholesteric liquid crystal phase. For example, as disclosed in Patent Literature 1, light of circularly-polarized light in one direction can be reflected selectively with high efficiency in the region of 700 to 1200 nm by forming one cholesteric liquid crystal phase on each surfaces of a λ/2 plate.
In addition, in Patent Literature 2, an infrared light-reflecting article having a cholesteric liquid crystal layer is disclosed. As to an infrared light-reflecting article using a cholesteric liquid crystal layer, there are many attempts for the utilization for liquid crystal display devices. Specifically, there are many attempts to cause light in the visible light region to be reflected effectively. For example, in Patent Literature 3, there is disclosed a liquid crystal display device in which a plurality of cholesteric layers are laminated.
In producing a film including a cholesteric liquid crystal layer, there is used, for example, a method in which a coated film containing a cholesteric liquid crystal material is dried, heated and aligned, and cured by ultraviolet rays. As to a method for curing a cholesteric liquid crystal layer, for example, as exemplified in Patent Literature 4, a method of curing a polymerizable liquid crystal compound by performing irradiation with ultraviolet rays is generally used, and there is disclosed a method for producing a cholesteric liquid crystal film with reflection wavelength of a broad region by adjusting illumination intensity within a certain range.
Here, in particular, for the intended use of the above-mentioned infrared light-reflecting article for automobiles, a high-quality film having good surface conditions and without unevenness is required. However, there is such a problem in which, when a film is produced by coating and drying a polymerizable liquid crystal composition containing a polymerizable liquid crystal compound, in particular, wind unevenness in drying (specifically, thickness unevenness in a film) is generated in a film to be produced (for example, see Patent Literature 5). In addition, similarly In Patent Literature 5, again, there are described a problem of the generation of unevenness also in a liquid crystal alignment when a polymerizable liquid crystal compound is aligned, and a problem of the generation of another problem of surface conditions (streaks in Patent Literature 5) in addition to wind unevenness in drying.
For problems of these various unevenness and surface conditions, in the invention described in Patent Literature 5, there is described a method for suppressing wind unevenness in drying by adding a fluorine-containing polymer as a compound having a function of preventing wind unevenness in drying to a coating liquid containing a liquid crystalline compound to thereby lower the surface tension thereof, and by causing the same to pass through a casing that is disposed with a condensation plate in initial drying immediately after the coating to thereby dry the same so that a boundary layer near the coated film is not disturbed.
On the other hand, in Patent Literature 6, as a method for producing a laminated film having two layers or more of a fixed cholesteric liquid crystal phase, there is described a method of repeating a step of coating a curable liquid crystal composition containing a rod-like liquid crystal compound, a fluorine-based alignment controlling agent of a specific structure and a solvent, and a step of drying the coated film to form a cholesteric liquid crystal phase, and after that, curing the same and fixing a cholesteric liquid crystal layer. In Patent Literature 6, attention is focused on coating repelling defect caused by an alignment controlling agent contained in the under layer of a fixed cholesteric liquid crystal phase when a second layer is formed, but attention is not focused on wind unevenness in drying of a coated film formed by coating a curable liquid crystal composition.